Projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction.
In a common operating mode, multimedia projection systems receive analog video signals from a personal computer ("PC"). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. A projection engine of these multimedia projection systems includes a light source, an image-forming device, and optical components for directing images onto a screen. The light source typically includes a replaceable lamp module for generating and directing light toward the image-forming device before it is projected on the screen. Lamp modules include a lamp-reflector assembly having a concave reflector and a lamp or burner accurately mounted near the focal point of the concave reflector. Because lamps have limited life expectancy, lamp modules are designed to be replaced in the field by a user of the projection system.
Significant effort has been invested into developing projectors producing bright, high-quality color images. However, the optical performance of conventional projectors is often less than satisfactory. For example, suitable projected image brightness is difficult to achieve, especially when using compact portable color projectors in a well-lighted room. The intensity of the light that can be generated by the lamp is one limitation of compact projectors. To maximize the intensity of light directed toward the image-forming device, an elliptical reflector is often used in the lamp-reflector assembly instead of a spherical or parabolic reflector. However, for optimal results, elliptical reflectors must be accurately positioned relative to a light-path aperture of the projection engine within true position and parallelism tolerances of approximately .+-.0.002 inch (0.05 mm), making it impractical to adjust the position of the lamp-reflector assembly after it is installed in the projector.
FIG. 1 shows an exploded view of a prior art lamp module 10 that includes a mounting bracket 12 having a pair of opposing channels 14 formed therein. Channels 14 are sized to slide onto mounting rails located within a projector (not shown) for precise positioning of mounting bracket 12 without the use of tools. A cover plate 16 is securely mounted to mounting bracket 12 and includes perforations that allow airflow generated by a fan within the projector (not shown) to pass through lamp module 10. A lamp-reflector assembly 18 is held securely in place against an adjustment plate 20 by a spring clip 22. Lamp-reflector assembly 18 includes a collar 24 having a flat face 26 that seats against pads 28 on the surface of adjustment plate 20 to fix the position of lamp-reflector assembly 18 along the X-axis. Collar 26 includes a groove (not shown) in which a key 30 on the surface of adjustment plate 20 fits to maintain the rotational position of lamp-reflector assembly 18. Because pads 28 and key 30 are formed in sheet metal, lamp-reflector assembly cannot be accurately positioned on adjustment plate within the desired tolerances.
Three screws 32 are inserted through three oversize holes 34 in adjustment plate 20 and threaded into three threaded holes 36 in mounting bracket 12. Oversize holes 34 allow the position of adjustment plate 20 (with lamp-reflector assembly 18 mounted thereon) to be adjusted by the manufacturer in the Y- and Z-directions during the assembly of lamp module 10. After adjusting the position of the adjusting plate 20, screws 32 are tightened to fix the position of adjustment plate 20 relative to mounting bracket 12. Typically the adjustment is performed while verifying the positional accuracy of lamp-reflector assembly 18 relative to mounting bracket 12. This verification is accomplished by sliding lamp module 10 onto a test fixture and measuring the position of lamp-reflector assembly 18 or the light generated by lamp-reflector assembly 18, relative to the test fixture.
Lamp module 10 is expensive to manufacture because mounting bracket 12, adjustment plate 20, spring clip 22, and screws 32 are all metal components. In particular, adjustment plate is difficult to manufacture due to the accurately sized pads 28 necessary to locate lamp-reflector assembly 18 in the X-direction. Heavy metal components are also undesirable because they cause the projector to be less portable, especially if a spare lamp module 10 is also carried. The individual adjustment of each lamp module 10 in the Y- and Z-directions during assembly also contributes significantly to the manufacturing cost of lamp module 10.